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Biomedical subjects

A Pearce

Publications and source records attributed to A Pearce.

At least 37 records · Page 2Linked to original sources
PubMed2000

Validation of scanning laser Doppler flowmetry against single point laser Doppler flowmetry in the measurement of human gastric serosal/muscularis perfusion.

BACKGROUND: Single point laser Doppler (LDF) has been employed intra-operatively to measure gastro-intestinal tissue perfusion, but despite reports that it may have a role in predicting post-operative complications consequent upon hypo-perfusion, methodological drawbacks have prevented its routine clinical application. Scanning laser Doppler flowmetry (SLDF) may address these drawbacks, but this new development has not been previously validated in human gastro-intestinal tissue. AIMS: This study assessed the ability of Scanning laser Doppler flowmetry to measure human gastric perfusion. METHODS: 10 patients undergoing oesophageal resection were studied. In each 6 measurements of gastric corporal serosal/muscularis were made over 30 seconds using the previously validated single point LDF technique. A single 1 cm2 SLDF scan was made of the same area prior to any vascular division. These measurements were repeated after partial gastric devascularisation and the two techniques' measurements then compared. RESULTS: Correlation between the 2 methods was good (coefficient of correlation was 0.955 (p<0.01). The mean bias (scan - single point PUs) was -3 PUs (95% CIs 16.3 to 45 PUs) and the limits of agreement were -64 to 58 PUs. The coefficients of variation for the 6 sets of single point measurements made in each patient ranged between 3.0% and 30.4% (mean = 12.5%). CONCLUSION: These results validate SLDF as a method of measuring gastric tissue perfusion intra-operatively.

Esophagectomy↗
PubMed1999

Intraoperative scanning laser Doppler flowmetry in the assessment of gastric tube perfusion during esophageal resection.

BACKGROUND: Ischemia from tissue hypoperfusion in the gastric tube after esophagectomy is believed to contribute significantly to postoperative complications associated with anastomotic failure. This study assessed the ability of the new technique of laser Doppler flowmetry to measure differential levels of blood flow in human gastric tubes during esophagectomy. STUDY DESIGN: Gastric perfusion was measured in 16 patients undergoing esophagectomy by making laser Doppler scans of the stomach before mobilization and after formation of the gastric tube. Mean perfusion was calculated within the whole anterior surface of the stomach or tube and within 1 cm2 regions of interest, each of which contained 1,750 individual measurements of perfusion. These regions represented the cephalic end of the gastric tube, 10 adjacent 1 cm2 regions distally along the tube, and the proposed anastomosis site. Results were expressed as mean perfusion units, and tissue blood flow from each scan in each region was compared. RESULTS: There were significant decreases in gastric perfusion measured with the scanning laser Doppler in all patients after formation of the gastric tube. Mean perfusion of the stomach fell 41% (p<0.0005) after mobilization. In all patients there was a gradient of perfusion from the proximal end of the tube where flow was poor, to more distal areas where it was higher. At the proximal end of the tube perfusion fell by a mean of 72%, 5 cm distally the mean fall was 44%, and 10 cm from the proximal end of the tube the mean fall was 28%. At the anastomosis site mean perfusion fell 55%. CONCLUSIONS: This new technique can be used intraoperatively and appears to overcome the limitations of single point laser Doppler flowmetry. It has measured large differences in perfusion at different sites within the gastric tubes and could therefore have widespread clinical applications.

Adult↗
PubMed1998

Scanning laser Doppler flowmetry and intraluminal recirculating gas tonometry in the assessment of gastric and jejunal perfusion during oesophageal resection.

BACKGROUND: The ability of the new techniques of scanning laser Doppler flowmetry and recirculating gas tonometry to measure changes in gastric serosal and mucosal blood flow respectively during oesophageal resection was assessed. METHODS: Changes in regional and total gastric blood flow were assessed in 16 patients undergoing oesophagectomy at three stages of the procedure. Laser Doppler images were analysed and perfusion expressed as mean perfusion units. Tonometric measurements of gastric and jejunal intramucosal pH (pHi) were made synchronously. RESULTS: There were significant falls in gastric perfusion measured with scanning laser Doppler flowmetry in all subjects between each measurement. Mean perfusion of the stomach fell 41 per cent after mobilization. There was a gradient of reduced perfusion between the antrum (mean fall 25 per cent) and the area used for the anastomosis in the fundus (mean fall 55 per cent). Before mobilization mean gastric and jejunal pHi were 7.37 and 7.46 respectively. These fell to 7.18 and 7.37 respectively after mobilization and to 7.29 and 7.38 after anastomosis. CONCLUSION: These new techniques could be employed at operation, appear to overcome the limitations of single-point laser Doppler flowmetry and saline tonometry, and have measured significant changes in gastric perfusion. They may have widespread clinical application.

Adult↗
PubMed1998

Children investigated for failure to thrive: where are they now?

Failure to thrive remains a common problem accounting for a large number of referrals to paediatric clinics. Some children with failure to thrive undergo extensive investigations including a sweat test to exclude cystic fibrosis. Selecting a group of children who had a sweat test, we chose to compare weight centile data recorded at initial presentation with data collected at routine school-entry medical several years later. It was encouraging to see that most children improved their weight centile with time, regardless of whether a diagnosis had been reached.

Child↗
PubMed1997

Unravelling the genetics of deafness.

Hearing-impaired mouse mutants not only are good models for human hereditary deafness, but also are extremely useful for understanding the molecular basis of the cochlear defect. We describe here how we identified the gene responsible for the deafness and vestibular defects in the shaker-1 mouse mutant as a myosin VII gene. Three different mutations, all causing the same phenotype in different lines of mouse, were found, providing good evidence that we had, indeed, found the correct gene. The same gene was subsequently found to be involved in Usher's syndrome type 1B, which features deafness, vestibular dysfunction, and progressive retinitis pigmentosa. The myosin VII gene is expressed in sensory hair cells, but not in supporting cells or neurons. We are investigating the role of myosin VII in hair cell development and function. Analysis of the different mutant stocks suggests it has at least two functions. First it is involved in the development and maintenance of the stereocilia bundle. Second, it has a role in inner hair cell function. No evidence of retinal degeneration like that in Usher's syndrome has been found in the shaker-1 mutants so far studied. The benefits of understanding the function of the gene for families with Usher's type 1B are discussed. This gene is the first to be identified as causing the most common type of disorder in human hearing impairment, neuroepithelial abnormalities, and suggests a new class of candidate genes for involvement in such defects.

Animals↗
PubMed1996

The Sp4H deletion may contain a new locus essential for postimplantation development.

Sp4H is a semi-dominant mutation that maps to mouse chromosome 1. Heterozygous mice exhibit white spotting of the belly, whereas the fate of the homozygous embryos is unknown. We have previously shown that the entire coding region of the Pax3 gene is deleted in the Sp4H mutant. In this study, we have analyzed the fate of the Sp4H homozygous embryos. No Sp4H homozygotes were detected by Southern blot or PCR analysis in 82 E9-E13-day embryos. We have also documented a significant increase in the number of resorption sites in Sp4H heterozygous matings compared to control litters. Sections of the resorption sites (moles) suggest that postimplantation development is arrested prior to gastrulation. We have mapped the extent of the deletion to a maximum of 1.53 +/- 0.6 cM using markers flanking the Pax3 locus. Four anonymous markers, D1Mit215, D1Mit253, D1Mit332, and D1McG156, have been shown to be deleted in the Sp4H mutation. Further nondeleted markers have been used to extend the linkage map of this region. A total of 22 loci were analyzed in a Splotch intraspecific backcross. Using these data and deletion mapping data, we predict the following order of markers: (D1Mit46, Vil)-(D1Mit79)-(D1Mit132, D1McG153)-(D1Mit332)-(D1-McG156, D1Mit253, D1Mit215, Pax3)-(D1Mit134)-(D1Mit8, D1Mit9, D1Mit44, D1Ler3, D1Mit183)-(D1Mit53, D1Mit82, D1Mit182)-(Bcl2). As the deletion is large enough to include other genes, and it seems that deletion of Pax3 is not likely to account for the early death of the embryos, we suggest that another developmentally important gene may be deleted in the Sp4H mouse mutant and that this may be responsible for the early death of the homozygous mutant embryos.

Alleles↗
PubMed1996

Affinity for the insulin-like growth factor-II (IGF-II) receptor inhibits autocrine IGF-II activity in MCF-7 breast cancer cells.

We have investigated the autocrine regulation of insulin-like growth factor-II (IGF-II) signaling by the insulin-like growth factor-I receptor (IGF-IR) and the insulin-like growth factor-II/mannose 6-phosphate receptor (IGF-IIR) in MCF-7 breast cancer cells, employing retroviruses encoding both IGF-I, IGF-II, and IGF-I and II mutants with reductions in affinity for either the IGF-IR or the IGF-IIR. These studies revealed reciprocal roles for IGF-IR and IGF-IIR affinity in the regulation of autocrine IGF-II activity. IGF-IR affinity was required for serum-free proliferation but also for efficient IGF-II secretion. In contrast, cellular proliferation, receptor tyrosine kinase-dependent signaling, and extracellular IGF-II protein accumulation were all reduced in the presence of IGF-IIR affinity. Inhibition of IGF-II signaling appeared to be the sole consequence of IGF-IIR affinity, as no cellular responses attributable to selective IGF-IIR binding by a reduced IGF-IR affinity IGF-II mutant could be detected. By operating as an IGF-II antagonist, the IGF-IIR has tumor suppressor-like properties, a suggestion consistent with reports of loss of heterozygosity at the IGF-IIR locus in a variety of human malignancies.

Amino Acid Sequence↗
PubMed1995

Recombinant GST/CD36 fusion proteins define a thrombospondin binding domain. Evidence for a single calcium-dependent binding site on CD36.

CD36 is a multifunctional cell surface glycoprotein that acts as a surface receptor for thrombospondin (TSP), and thereby may mediate adhesive interactions between cells and substrata, platelets and other cells, and macrophages and apoptotic neutrophils. The identity of the TSP binding site on CD36 is controversial and may involve more than one structural domain. We have constructed a series of recombinant bacterial GST/CD36 fusion proteins that span nearly all of the CD36 molecule and have demonstrated that fusion proteins containing the region extending from amino acid 93 to 120 formed specific, saturable, and reversible complexes with TSP. As with intact CD36, binding was calcium-dependent, was independent of which ligand was immobilized, and was blocked by monoclonal antibodies to both CD36 and TSP. Stoichiometry and affinity of the fusion proteins for TSP were consistent with that of the intact protein. We also demonstrated that these fusion proteins competitively inhibited binding of TSP to purified platelet CD36 and to cell surface CD36 on peripheral blood monocytes and CD36 cDNA-transfected melanoma cells. These data demonstrate that the region between amino acids 93 and 120 has all of the characteristics required of the TSP binding domain.

Antigens, CD↗
PubMed1995

Oxidized LDL binds to CD36 on human monocyte-derived macrophages and transfected cell lines. Evidence implicating the lipid moiety of the lipoprotein as the binding site.

Accumulating evidence strongly implicates oxidized LDL (Ox-LDL) in the pathogenesis of atherosclerosis. Several receptors have been identified that bind and internalize Ox-LDL, but their relative importance in vivo is unclear. CD36 is an 88-kD transmembrane glycoprotein expressed on monocytes/macrophages, platelets, and microvascular endothelium that has been implicated as a putative receptor for Ox-LDL. We demonstrate that an anti-CD36 monoclonal antibody inhibited 50% of the specific binding and 26% of the specific degradation of Ox-LDL by human monocyte-derived macrophages. To characterize more completely this binding we evaluated interactions between CD36 and Ox-LDL in murine NIH-3T3 cells stably transfected with human CD36 cDNA. Ox-LDL bound to CD36-transfected 3T3 cells in a saturable manner. Specific binding, internalization, and degradation of Ox-LDL were increased fourfold in CD36-transfected cell lines compared with 3T3 cells transfected with vector alone. Binding of Ox-LDL to CD36-transfected 3T3 cells was inhibited by a panel of anti-CD36 antibodies and by soluble CD36 but not by thrombospondin. Specificity of binding was demonstrated by the equivalent binding of LDL and acetylated LDL to control and CD36-transfected 3T3 cells. The epitope or epitopes on Ox-LDL recognized by CD36 are undefined. Two observations suggest that CD36 recognizes a lipid moiety or that the lipid portion of the lipoprotein is essential for apoprotein recognition. The first is that the increased binding of Ox-LDL to CD36-transfected 3T3 cells is abrogated by delipidation of the lipoprotein, and the second is that oleic acid competes for the binding of Ox-LDL to CD36-transfected 3T3 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗
PubMed1995

Regulation and targeting of T-cell immune responses by IgE and IgG antibodies.

A set of chimeric antibodies with identical F(ab')2 fragments specific for the hapten 5-iodo-4-hydroxyl-3-nitrophenacetyl (NIP), but with different human Fc parts (gamma 1, gamma 2, gamma 3, gamma 4, epsilon), was used to compare the role of IgG and IgE antibodies in antigen presentation by human Epstein-Barr virus (EBV) B cells. Two or three molecules of NIP were coupled to one molecule of Der pI (Der pI-(3)NIP), a major allergen of Dermatophagoides pteronyssinus. Both monomeric IgG and performed complexes of various Der pI/IgG ratios failed to bind significantly to the Fc receptor for IgG on B cells (Fc gamma RII; CD32). Binding of IgG3 (> IgG1)-containing complexes (optimal ratio of antigen to antibody = 1:1) could be enhanced by increasing the number of haptens per Der pI molecule to nine or more. However, antigen presentation mediated by IgG and CD32 was not seen with either pulsed B cells or B cells that were allowed to capture the IgG complexes during the whole stimulation period. IgE binding to CD23 and subsequent IgE-mediated antigen presentation was seen under all conditions tested. Even monomeric immune complexes (IC) (Der pI-(3)NIP/IgE), in the absence of CD23 cross-linking, induced an immune response. As the number of natural epitopes for human antibodies on Der pI was less than five, we conclude that, in vivo, complexes consisting of Der pI/IgG will be directed to antigen-presenting cells expressing the high-affinity receptor for IgG (CD64), whereas IgE will allow antigen presentation by CD23-expressing cells, including B cells.

Allergens↗